Explain the term ground waves propagation of radio-waves.

Explanation

Ground wave propagation : When the radio waves from the transmitting antenna propagate along the surface of the earth so as to reach the receiving antenna, the wave propagation is called ground wave propagation.
The transmitted radio wave is supported at the lower edge by the ground. The radio waves have to be vertically polarised so as to prevent the short circuiting of the electric field component of the wave. The radio wave induces current in the ground over which it passes. It attenuates to some extent due to some energy absorption by the ground.
The surface wave gets attenuated due to one other reason also. As the wave propagates over the earth, it gradually tilts over. It is called diffraction effect. At some distance from the transmitting antenna, the wave .lies down and dies.. The maximum range of such a transmitter depends on its frequency as well as its power. Surface wave propagation is of importance only for medium and long wave signals. All amplitude modulated radio signals received in daytime propagate by means of surface waves. For TV and FM signals (signals of very high frequency), the ground wave propagation is not used. It is because. at high frequency, the ground wave signal is so reduced in strength by absorption that it virtually becomes useless beyond an area of a few kilometres around the transmitting antenna.